1. Field of the Invention
This invention relates generally to the formation of cross-laminated non-woven fabrics and more particularly to a method of and an apparatus for heat-setting such a fabric without involving widthwise shrinkage.
By the term "cross-laminated non-woven fabric" used herein is meant a fabric resulting from crosswise lamination of a warp web and a weft web and tending to shrink upon exposure to heat particularly in the transverse direction. The term "heat setting" denotes a process step which allows for bonding of the above laminate into an integral structure while preventing the weft web from becoming widthwise shrunk and also for annealing the laminate to alleviate shrinkage of the weft web in the transverse direction.
2. Description of the Prior Art
Fabrics of a cross-laminated non-woven structure and sheets of a cross-laminated type have of late been developed and marketed. In the manufacture of such products, their respective warp and weft webs are superimposed one on the other and thereafter required to be successively set with heat without objectionable shrinkage caused widthwise relative to the line of production or to the direction of movement.
Both woven and nonwoven types of fabrics need to be heat-set to reduce heat shrinkability. A cross-laminated non-woven fabric, however, should be by nature subject to heat setting under relatively strict conditions as it is liable to shrink widthwise to a larger degree than a nonwoven fabric and hence responsible for unsightly appearance. Further, the fabric in question calls for firm bonding of the warp and weft webs at a high level and economical and efficient means for heat setting even in a speedier line of production.
A tentering system is known for use in the heat setting of a sheet-like product such as for example a stretched film or reticulate material. This treatment is done usually with two opposite sides of the sheet engaged with pins or clips. Although capable of heat-setting the sheet free from widthwise shrinkage, the system of tentering is undesirable for commercial application because, due to heating being dependent on hot air, it is rather bulky and spacious and hence feasible costly and moreover thermally inefficient. In the case of a non-woven fabric in which warp and weft webs are cross-laminated, firm bonding of both webs is made difficult to achieve with the above mode of heat setting.
To produce a cloth-like material by cross-laminating warp and weft webs, it has been proposed to effect fixation or otherwise adhesion on a hot rotating cylinder as disclosed for instance in U. S. Pat. No. 4,052,243. In this prior arrangement a continuous row of weft webs each severed to a length equivalent to the width of a warp web to be laminated is crosswise laid over or even beneath the latter web continuously fed to travel in the longitudinal direction. The resulting laminate is dried and fixed as it is successively guided around a rotating cylinder heated. Such arrangement is contrieved to attain improved efficiency of operation from crosswise lamination of the warp and weft webs to subsequent drying and adhesion. There is no suggestion in the above patent to cope with widthwise shrinkage which may occur during heat setting of highly oriented cross-laminated non-woven fabrics. No means in fact is provided for that purpose.